PALEO-ENVIRONMENTS AND THE HUMAN OCCUPATION OF QUEBRADA MANI, NORTHERN ATACAMA DESERT, CHILE

Quebrada Maní is a hyper-arid watershed in the southernmost Pampa del Tamarugal region of the Atacama Desert, Chile. Surficial geologic mapping and dating of a 4.75 km segment of Quebrada Maní and paleowetland deposits within the catchment, were initiated to reconstruct past environments associated with Proto Archaic (ca. 12.8-11.6ka) and early/late Formative (ca 2.5 to 0.7ka) archaeological sites. Five distinct stratigraphic units (B1, B2, B3, D1, and D2) were identified adjacent to the archaeological sites. Late Pleistocene paleowetland deposits comprise Units B1 (ca. 17,600-16,600) and B3 (ca. 11,100-9,400 cal yrs BP), which are separated by an unconformity (Unit B2). The paleowetland deposits correspond with the Tauca and Coipasa pluvial phases of the Central Andean Pluvial Event (CAPE). During the deposition of Unit B1 at 1250m, a large alluvial fan system comprised of gravels, cobbles, and boulders with braided streams cutting westward, dominated the Maní catchment. The unconformity marking Unit B2 is comprised of eolian sand channel infill and represents a period of pronounced aridity corresponding to the Bølling-Allerød interstadial. Deposition of Unit B3 occurs alongside a change in base-level which influenced the incision of perennial streams as well as the appearance of wetland deposits down slope at 850m. At this time, Quebrada Maní is seasonally inhabited by Proto Archaic hunter-gatherers migrating back and forth from the coast to the Andes. Stream aggradation, associated with a positive hydrologic budget, occurred ca. 2730-2230 and 1730–1610 cal yrs BP (Unit D1) as well as 930–690 cal yrs BP (Unit D2), corresponding with evidence for early/late Formative human habitation. Despite intermittent periods of stream aggradation, an overall drop in base-level over the Holocene created deeply incised ephemeral streams dominated by the occasional hyper-concentrated flow event and the absence of vegetation. Mudflows become the dominant form of sediment transport throughout the catchment, while landscape deflation down slope exposes remnants of B3 wetland deposits over a meter above the deflated surface. Past climate change facilitated the settlement of the Atacama by early hunter-gatherers and early/late Formative agriculturalists along fluvial drainages in an otherwise barren landscape.